The invention relates to a pump having a shaft, an impeller arranged on the shaft, and a labyrinth seal arranged between stationary and moving parts of the pump. The invention also relates to a fuel cell system having a pump such as this.
Swiss patent document CH 134 440 discloses a labyrinth seal between stationary and moving parts of a pump. The labyrinth seal has pointed spurs which are separated by a minimal gap and are arranged in the direction of a disk which is mounted on the shaft. The tips of the labyrinth seal are therefore arranged essentially parallel to the axis of the shaft.
Furthermore, German patent document DE 103 14 820 A1 discloses a method for preventing water from freezing in the anode circuit of a fuel cell system, as well as a fuel cell system. The fuel cell system has a recirculation pump which may be in the form of a side-channel compressor. This has a shaft and an impeller, which is arranged on the shaft and has a plurality of blades.
An impeller area which is formed between the shaft and a blade rear is in the form of a cavity which is closed at the top by a pump housing. The blade rear facing the shaft is formed without any corners and opens, in particular in the form of a curve, into the surface of the impeller.
In an entirely general form, side-channel compressors such as these are formed with an impeller such that there is a relatively small space between the moving components and the stationary components. This is used as a closure or seal during operation of the pump, and improves the pump efficiency. If the pump is designed to feed gases, then, in particular, a problem can occur as a result of these intermediate spaces during starting of the pump, if liquid enters these intermediate spaces when the pump is deactivated. For example, this liquid may be condensation which is formed when the pump is in the deactivated state. Furthermore, if the pump is used in environmental conditions which are characterized by relatively low temperatures, in particular close to or below the freezing point of water, then the pump can freeze. In this case, the movable parts of the pump can be frozen to the stationary parts by the freezing water in the intermediate space. This can make it impossible to start the pump, or at least make it very difficult. The increase in the volume of the freezing water can likewise result in damage to components of the pump.
One object of the present invention, therefore, is to provide a pump (and a fuel cell system having such a pump) in which it is possible to prevent liquid from accumulating in the area of the pump impeller. One particular aim is to prevent the impeller from freezing to the labyrinth seal, and therefore also to stationary parts of the pump.
This and other objects and advantages are achieved by the pump according to the invention, which has a shaft and an impeller arranged thereon. Furthermore, the pump has a labyrinth seal which is arranged between stationary and moving parts of the pump. In particular, the labyrinth seal is arranged fixed to a housing of the pump, and is positioned in the immediate vicinity of the impeller. A plurality of blades are arranged on the impeller, with the labyrinth seal, which extends at least between the shaft and a blade rear of the blades, having a channel which extends in a helical shape.
A refinement such as this in particular to the channel of the labyrinth seal allows the water accumulating in the area of the impeller to be reliably carried away out of the intermediate spaces between the labyrinth seal and the impeller. The helical extent of the channel ensures that the water is transported away in a particularly effective and efficient manner. Water residues in the area of the impeller can therefore be virtually completely prevented. This also makes it possible to prevent the impeller from freezing hard on the labyrinth seal at low environmental temperatures, avoiding the problems in starting the pump. Not least, this also makes it possible to prevent water freezing in the area of the impeller and of the labyrinth seal expanding and leading to damage to components of the pump, in particular of the impeller and of the labyrinth seal.
At least one channel of the labyrinth seal is preferably formed on the casing side of the labyrinth seal. The impeller is preferably in the form of a disc, and the labyrinth seal has an annular shape. Since this annular structure has a certain height this therefore also forms a casing surface, in which case the water can be effectively transported away by this relatively external configuration of the channel in the labyrinth seal.
It is particularly advantageous for the pump to be in the form of a side-channel compressor and to have at least one side channel in which the water can then be transported away. The channel in the labyrinth seal thus preferably leads into at least one side channel of the pump. The pump preferably has an upper and a lower side channel.
It is particularly advantageous to consider the channel in the labyrinth seal to be in the form, in its longitudinal extent, of a channel which is open at the side in the casing side of the labyrinth seal, and for the blade rears to form a channel wall once the labyrinth seal has been inserted into the pump.
The channel in the labyrinth seal is preferably formed with an essentially constant radius and in particular is designed to be circumferential around the axis of the shaft.
In particular, the channel of the labyrinth seal is designed to complete at least two revolutions around the shaft axis. The channel may, of course, also have a plurality of helical turns.
Those areas of the labyrinth seal which face the blade rear are preferably tapered. In particular, those areas which face the blade rear are in the form of points.
A refinement such as this minimizes the area of the labyrinth seal which is arranged immediately adjacent to the wall of the blade rear. This makes it possible to implement refinements in which as little surface area as possible is created on which water can accumulate, and freeze firmly there, in the intermediate space between the labyrinth seal and the blade rear.
In particular, a pointed refinement such as this of subareas of the casing surface of the labyrinth seal makes it possible for the channel in the labyrinth seal to have a triangular cross section.
It should be noted that the channel in the labyrinth seal results in a channel whose cross section is not completely closed. This is because the casing surface, or the side of the labyrinth seal facing the blade rear, is not intended to rest directly on this blade rear. A minimal gap is provided between the wall of the blade rear and the casing side of the labyrinth seal. However, this formation of an intermediate space is in general sufficiently small that it cannot effectively be regarded as an outlet opening when the water is being transported away through the channel of the labyrinth seal. A negligible leakage of the water to be transported away therefore invariably occurs through this intermediate gap.
It is also possible for those areas of the labyrinth seal which face the blade rear to be flat. In a refinement such as this, there are therefore larger areas of the casing side opposite the labyrinth seal and the surface of the blade rear.
In a refinement such as this, the channel of the labyrinth seal is preferably designed to have a quadrilateral cross section.
That surface of the impeller which faces the labyrinth seal is preferably structured at least in places with a roughness which is greater than that of a further surface of the impeller. A rough impeller surface such as this can be achieved by allowing liquid droplets to flow into the depressions in the structuring, at least in places, thus making it possible to keep the height of these water droplets projecting above the surface of the impeller small. Furthermore, such rough structuring with relatively small depressions makes it possible to enlarge the surface area, as a result of which the remaining liquid droplets once again also remain in the depressions of a relatively large surface area, because of their surface tension. This refinement as well makes it possible to reduce the probability of movable parts freezing firmly to stationary parts in the pump since, even if the water droplets remain in the pump, they are relatively flat.
That surface of the impeller which faces the labyrinth seal is preferably coated, at least in places, with a metal layer which has greater roughness than a further surface of the rotor. In particular, a sprayed-on metal layer coating can be provided. This particularly effectively ensures the advantages already mentioned above with regard to reducing the height of liquid droplets. Furthermore, a metal layer such as this is also subject to little wear.
That side of the labyrinth seal which faces the impeller is preferably structured at least in places with a greater roughness than a further surface of the labyrinth seal. This also makes it possible to take positive account of the advantages mentioned above with regard to the liquid distribution.
The surface of the labyrinth seal is advantageously coated at least in places with a hydrophobic material. In consequence, the cohesion forces of a liquid are a primary factor, in comparison to other forces. In particular, areas of the labyrinth seal which taper at the side or are even pointed, and which face the blade rear, make it possible to ensure that the liquid which still remains automatically runs away from these points and runs into the interior or the troughs of the channel. A hydrophobic coating such as this therefore automatically makes it possible for the remaining water to move away into the interior of the channel, from the intermediate space between the labyrinth seal and the blade rear.
Once again, this therefore makes it possible to reduce the amount of water located directly in the space between the labyrinth seal and the blade rear, and therefore to avoid the possibility of firm freezing.
Furthermore, the hydrophobic coating in the case of a channel with a helical shape, in particular in conjunction with pointed outer faces, makes it possible to reduce the adhesion, and the friction of the hydrophobic material allows the liquid to flow away out of the intermediate space, just by gravitational forces.
The impeller, which is in the form of a disc, is preferably designed such that its cross section tapers in the direction of the blade rear. The upper face of the impeller preferably runs such that it falls in the direction of the blade rear. A refinement such as this therefore also makes it possible to assist the process of the liquid which is accumulated in the area of the impeller flying away in the outward direction toward the blade rear.
It has been found to be particularly preferable for the junction between the surface of the impeller and the blade rear to be formed without corners. In this case, a continuous curvature is preferably provided. Once again, and in conjunction with the helical channel in the labyrinth seal, this makes it possible to positively influence the process of transporting water away.
A further aspect of the invention relates to a pump having a shaft and an impeller which is arranged on the shaft, and having a labyrinth seal which is arranged between stationary and moving parts of the pump. A plurality of blades are arranged on the impeller, and a blade rear of the blades and a side facing the blade rear, of the labyrinth seal, which extends at least between the shaft and the blade rear, are formed at an angle to the rotation axis of the impeller, and the side which faces the blade rear, of the labyrinth seal, and/or the blade rear are/is stepped at least in places in order to form a stepped channel extending between them.
A refinement such as this, in particular of the channel in the labyrinth seal, makes it possible for water which has accumulated in the area of the impeller to be reliably carried away from the spaces between the labyrinth seal and the impeller. The stepped extent of the channel makes it possible to ensure that the water is transported away particularly effectively and efficiently. Water residues in the area of the impeller can therefore be virtually completely avoided. In consequence, it is also possible to prevent the impeller from freezing firmly on the labyrinth seal at low environmental temperatures, and to avoid pump starting problems. Not least, this also makes it possible to avoid water which is freezing in the area of the impeller and of the labyrinth seal expanding and leading to damage to components of the pump, in particular of the impeller and of the labyrinth seal.
The inclination of the side of the labyrinth seal and/or of the blade rear with respect to the rotation axis of the impeller is preferably at an angle of greater than 0 and less than 90 degrees. This allows the water to be driven out particularly effectively. It is also possible to provide an angle of greater than 0 and less than 180 degrees.
The channel is preferably in the form of a staircase. The water can be driven outwards with the aid of the centrifugal force when the impeller is rotating. The labyrinth seal is then no longer formed just with horizontally running sides. The angled arrangement mentioned above can then be used to produce a labyrinth gap which is in the form of a staircase and does not run vertically. The length of the gap and its geometry can in this case be lengthened and configured in many ways. In one optimum refinement, the gap losses, inter alia, are also minimized, and the effectiveness of the labyrinth seal is maximized.
The walls which form a step are preferably arranged at an angle of greater than 0 and less than 180 degrees to one another.
The pump according to the invention in the first aspect, or an advantageous embodiment of it, can also be combined with the pump according to the invention of the second aspect, or an advantageous embodiment thereof.
In an entirely general form, in the case of the two aspects of the pumps according to the invention, the gap in the labyrinth seal, in particular, is designed such that liquid water can be actively carried away, in which case, for this purpose, the labyrinth seal is formed at least in places with a channel which is helical and/or in the form of a staircase, or forms at least a part of the channel.
A further aspect of the invention relates to a fuel cell system having at least one fuel cell and one pump according to the invention, or an advantageous refinement thereof. The fuel cell system is preferably in the form of a mobile fuel cell system and, in particular, can be arranged in a motor vehicle.
In particular, a fuel cell in the fuel cell system is in the form of a PEM fuel cell.
The pump is preferably associated with the anode branch of the fuel cell. The pump is in this case preferably arranged in a recirculation circuit in the anode branch. The off-gas produced by the anode of the fuel cell is fed back via the recirculation circuit.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.